V6 Camaro.

If you can't build a pretty basic, but decent one, for around $8k then you're not trying hard enough. Plentiful parts, high quality ones too, at low prices. Good weight distribution, good brakes, and they did AutoX well back in the day.

Competitive? Not sure, but I think the power is going to be there for you. Live rear axles are not as henious as people make them out to be in IT (ask Jeff Young), and you'll have fun I bet!

You can then join the ITR Domestic Brigade, spoiling the look of IT.